Gould OS4000 Storage oscilloscope - UK Vintage Radio Repair and Restoration Discussion Forum

ProDave · 5th Dec 2007, 10:55 pm

My trusty old Gould OS4000 storage scope has just packed up. I need some help to fix it. It worked fine one day, next day when turned on it was broken.

Firstly does anyone have a link to a service manual for it?

Here's a description of the fault. It outwardly appears completely dead apart from the "power" light comes on. Nothing else works. No trace on the tube, none of the various LED's that indicate thinks like trigger modes light up under any conditions, and even the scale illumination lamp does not work.

Sounds easy? a power supply problem. No. All outputs from the main power supply panel test okay. The tube heaters are working.

So so far I have only looked at the panel that controls the scale illumination (since that is not working, this seems an obvious place to start) This also appears to produce the CRT HT (which I have not checked). I haven't done much yet, other than some basic checks on usual suspects like high power resistors, and no obvious faults.

So I guess I first at least need the circuit diagram of this panel. Then some inside information on how the hell you get at it. There are several panels all stacked vertically and this is the inside one of the stack, so all you can see is it's top edge. No obvious way to just unplug it. It really looks a major major job to dismantle the whole chassis just to seperate out the various boards. Then how do you power up the scope once dismantled for any meaningful testing?

It really does look a servicing nightmare, so any hints and tips much appreciated.

valveaudio · 6th Dec 2007, 4:47 pm

Hi,
I also have a OS4000 that is sick, mine sometimes works for a few seconds and then no trace, so far I found that it has no time base, but the clock osc. is running and all indications are ok.
I understand what you have said about accessability, it is a major job and it looks as though to gain access to some boards you may have to remove the tube.
I would suggest that you have a look at the dil connectors as a start, they do seem to get very dirty.

Mauritron have the manual (download £10) I have not bothered since I now have 3 working scopes, maybe when I have a lot of time----

If you would like me to make any measurements let me know, it seems that your fault is rather different than mine.

Good luck
Trevor

Chris55000 · 6th Dec 2007, 5:50 pm

Hi!

Watch this space....schematics/repair hints are coming as soon as I've fixed my Gaffer's PC, hopefully 2nite!!!

Many thanks,

Chris Williams

Chris55000 · 20th Dec 2007, 10:44 pm

Hi!!!

Virgin Media had done their worst again & I've also had a dose of the flue, so I was unable to get straight back on this!!!

***WARNING!!!*** The Gould OS4000 uses -1000V and +3000V supplies obtained from an EHT mains-transformer winding and a shock from either of these points ***CAN KILL!!!***. If you've ***any*** doubts about the following tests, either ask if someone can repair your instrument for you, or *contact me in the New Year* and I'll see about bringing my '4000, manual & gear & have a look at it myself *your convenience* @ your place!!!

1) To begin with, you need to check the mains transformer is OK. '4000 Squigglegraphs use a single transformer T51 that provides everything, EHT included (from a multiplier circuit), so start by making sure the 850V EHT source winding is OK. If this OK then check the +20V and +170V supplies are correct on the EHT PCB Assembly No. 36009, as without this the EHT series regulator TR402/TR403 can't function, and the EHT secondary return-path will be o/c!!! The HT+170V line has a 250mA fuse FS501 protecting it, if this has gone west you'll need to check the X/Y amplifier stages (I'll cover this in a later post).
The +20V supply comes fron IC503 on PSU Board 36015, if this is low or missing disconnect each of the feeds off the three "+20V" points in turn, if disconnecting any of these restores the +20V then you need to investigate in more detail with a current-limited bench PSU to find the fault as three terminal regs simply shut-down if overloaded!!!

2) If the +20V & +170V on EHT PCB 36009 are OK, then check across C402 (+ and - terminals of BR401) for approx. 145V d.c., and check the "Set EHT" preset R409 will adjust this, if not check TR402/TR403 for short or open circuits and make sure R409 isn't itself dud!!!
Next, check on the "-1kV" point with a ***good high-voltage meter or DMM with a suitable EHT probe of known safety and reliability***, if this is low or missing check D404-406 (1N4007) & C404, C406 & C407 (4uF 450V, use 4u7 as replacements). The +3kV supply uses three SCM30 3000V PIV diodes & 4 x 0u01 2000V capacitors C410-C413 in a trebler arrangement - dud diodes can be replaced with BY8412s, BY176s, BYX10-1600 or RGP20-02 depending on what you can get - anything with a min. PIV of 3000V @ 10-20mA'll do!!!

This is Part 1, let us know what you've got so far so I can sort out the most relavent bits of manual to post next!!!

Chris Williams

ProDave · 5th Jan 2008, 11:01 pm

Hi Chris

thanks for all that. there's a lot of information there to digest.

Don't wory about taking a long time to post it. I haven't been able to do anything for a few weeks as my workbench has been full with a project, and then we went away over the xmas / new year period. Now I'm back and my workbench is clear, I can finally get round to trying to fix the 'scope (when I get some time).

I will probe all the voltage tests as a start and let you know what I find.

As a very unscientific test, I did observe that one WW resistor on the board that controls the scale illumination was stone cold after the scope had been on for several minutes, implying no current flowing through it. I'll see if I can identify it as that may help.

I'll report back when I have done some tests.

Many thanks for all the help so far.

ProDave · 7th Jan 2008, 9:31 pm

All fixed now. Many thanks.

Thanks to your help, I removed the two logic boards into their service position. A task that is infinitely easier than it looks at first. But as it turned out, in my case this was unnecessary.

I did all the voltage checks you sugested (except the 3KV as I don't have a meter that goes that high) and all were okay.

But the fault was soon found. It turned out to be BR55 which provides the +5V and -3V supplies was O/C. Obvious really that a digital 'scope won't peform if it's main logic power supply voltage is missing. This bridge rectifier is mounted directly on the mains transformer (as are all of them)

I missed these two voltage tests on my initial blind testing as their test points on the power supply board were not very clearly marked. (by blind testing, I mean my initial probing around to check power supply voltages without the benefit of a circuit diagram or any other service information)

So once again many thanks, my trusty old 'scope lives on.

Chris55000 · 9th Jan 2008, 1:17 pm

Hi!

Good Show! Pleased to be of assistance! I'll post more manual when I've got my PC going again - it's m/b has just died!

Chris Williams

ProDave · 9th Jan 2008, 1:21 pm

Just a quick follow up. I do notice the replacement bridge rectifier (still mounted on the transformer) runs quite hot. I'm sure the replacement is adequately rated, but I don't like semiconductors that run hot. So in the hope of improving reliability, I am going to mount the new BR on the back panel, so it can benefit from the heatsink.

jaegerh · 9th Feb 2008, 7:14 pm

Hi Chris and Dave,

I also own a Gould OS4000 with some hiccups. Thanks to search engines I found your thread ... very lucky.
Since those few scanned pages from the service manual did already help me some way, I am still missing essential information. I wonder if you could help me out?
The error on the scope looks as follows:
It seems to work fine, but the x-deflection at the 5ms/div to .1ms/div timebase range is totally offset. The trace is shifted about half a screen to the right.
I guess it is just one component common to those timebase settings, or a contact in the rotating switch.
But before I open the thing up, I would like to have a look at the schematics and service manual, otherwise I don't think I can trace it down. I would also like to check the calibration if the repair is successful.
What I really like about this scope is its fanless design, and I hope I can make it fully operational again.
I hope you (especially Chris) can help me out with some more scanned pages..

Thanks,

Herbert

Chris55000 · 9th Feb 2008, 11:25 pm

Hi!

More manual coming up tomorrow......!!!

Chris Williams

Chris55000 · 10th Feb 2008, 8:16 pm

Hi!

Manual Part 2......!!!

Chris Williams

Chris55000 · 10th Feb 2008, 9:43 pm

Hi!

Manual Part 3......!!! I'm afraid this's all I can manage for now otherwise I'll not be up for work in the morning!

Chris Williams

jaegerh · 15th Feb 2008, 6:56 pm

Chris, thank you very much for spending the time.
I will definitely read through the documents asap, hopefully I have the time next weekend to get to the hardware..I will tell you how it went.
Thanks again!

Herbert

ProDave · 22nd Feb 2008, 1:36 pm

Many thanks Chris. All those files stored away for next time the 'scope breaks down.

Chris55000 · 22nd Feb 2008, 8:29 pm

Hi!

Manual Part 4......!!!

Chris Williams

Chris55000 · 22nd Feb 2008, 9:07 pm

Hi!

Manual Part 5......!!!

Chris Williams

Chris55000 · 22nd Feb 2008, 9:32 pm

Hi!

Manual Part 6......!!! Thats about it I think!!! Please accept my apologies for
the Circuit Diagrams being in two chunks - I'm afraid I've not got the loot for
an A3 Scanner yet!!!

I can only suggest a Bit Of Panoramic Stitchery With An Image Editor Or Good
Old-Fashioned Sellotape & Scissors For Now!!!

Chris Williams

ProDave · 29th Feb 2008, 2:10 pm

Once again, Many thanks Chris for taking the time and trouble to post all that.

jaegerh · 25th Mar 2008, 5:37 pm

Great news folks!

I had plenty of time over the easter holidays, and with the complete manual at hand (Thanks Chris!) I started to search the fault.

And, voila, one of the hold-off capacitors at switch s6dB showed around 500 Ohms instead of 47pF, thus completely upsetting the bias poins in the timebase sweep generator.

Now I am really happy to have it fully functional again; I also cleaned the front panel and knobs from previous owners - the scope looks like new now.
Calibration is still missing, but I will have to do that at work one evening - that's where the good test equipment lives.

By the way, my Gould 4000 has also the OS4001 Output Unit attached to it, which made access to all boards more complicated. The scope does not work with the OS4001 disconnected.
Chris, do you have the manual for that as well? I have no clue how to operate it, but I will probably never use it anyway.

I have put together the complete circuit diagrams. The scan alignment was good, I didn't even have to rotate them. Please find the files in the attachment - I tried to keep the image quality while meeting the 1.9Mb upload size constraint. You will need an A3 printer for a legible output.

Chris, page 75 is titled 'Interconnections (Contd.)' - is there more to it?
Also, the component listing is missing for the interconnection diagram. The faulty capacitor was C92 from that schematic, but fortunately the value was printed on it. Could you please scan that if you have the time?

Thanks again for all the effort, you really helped me to a nice success experience -

Herbert

PS - sorry folks, I experience difficulties attaching files even though they are not too big - hopefully I will be successful later.

Chris55000 · 26th Mar 2008, 1:21 pm

Hi!

Yes, I have repair words for the '4001 thingy but my PC's kicked the bucket again - a friend's going to fix it whilst I'm on holliers next week!!!

There's not a lot of it, I'll see if I can get it done before I go to my Sister's at the weekend!!!

Chris Williams

PS!!! I think I've done all I had but I'll double-check the "interconnections" bits list tonight in case I've missed an odd bit out!!!

5th Dec 2007, 10:55 pm	#1
ProDave Retired Dormant Member Join Date: Sep 2007 Location: Inverness Posts: 24	Gould OS4000 Storage oscilloscope My trusty old Gould OS4000 storage scope has just packed up. I need some help to fix it. It worked fine one day, next day when turned on it was broken. Firstly does anyone have a link to a service manual for it? Here's a description of the fault. It outwardly appears completely dead apart from the "power" light comes on. Nothing else works. No trace on the tube, none of the various LED's that indicate thinks like trigger modes light up under any conditions, and even the scale illumination lamp does not work. Sounds easy? a power supply problem. No. All outputs from the main power supply panel test okay. The tube heaters are working. So so far I have only looked at the panel that controls the scale illumination (since that is not working, this seems an obvious place to start) This also appears to produce the CRT HT (which I have not checked). I haven't done much yet, other than some basic checks on usual suspects like high power resistors, and no obvious faults. So I guess I first at least need the circuit diagram of this panel. Then some inside information on how the hell you get at it. There are several panels all stacked vertically and this is the inside one of the stack, so all you can see is it's top edge. No obvious way to just unplug it. It really looks a major major job to dismantle the whole chassis just to seperate out the various boards. Then how do you power up the scope once dismantled for any meaningful testing? It really does look a servicing nightmare, so any hints and tips much appreciated.

6th Dec 2007, 4:47 pm	#2
valveaudio Hexode Join Date: Feb 2006 Location: Diss, Norfolk, UK. Posts: 386	Re: Gould OS4000 Storage oscilloscope Hi, I also have a OS4000 that is sick, mine sometimes works for a few seconds and then no trace, so far I found that it has no time base, but the clock osc. is running and all indications are ok. I understand what you have said about accessability, it is a major job and it looks as though to gain access to some boards you may have to remove the tube. I would suggest that you have a look at the dil connectors as a start, they do seem to get very dirty. Mauritron have the manual (download £10) I have not bothered since I now have 3 working scopes, maybe when I have a lot of time---- If you would like me to make any measurements let me know, it seems that your fault is rather different than mine. Good luck Trevor

6th Dec 2007, 5:50 pm	#3
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,873	Re: Gould OS4000 Storage oscilloscope Hi! Watch this space....schematics/repair hints are coming as soon as I've fixed my Gaffer's PC, hopefully 2nite!!! Many thanks, Chris Williams

5th Jan 2008, 11:01 pm	#5
ProDave Retired Dormant Member Join Date: Sep 2007 Location: Inverness Posts: 24	Re: Gould OS4000 Storage oscilloscope Hi Chris thanks for all that. there's a lot of information there to digest. Don't wory about taking a long time to post it. I haven't been able to do anything for a few weeks as my workbench has been full with a project, and then we went away over the xmas / new year period. Now I'm back and my workbench is clear, I can finally get round to trying to fix the 'scope (when I get some time). I will probe all the voltage tests as a start and let you know what I find. As a very unscientific test, I did observe that one WW resistor on the board that controls the scale illumination was stone cold after the scope had been on for several minutes, implying no current flowing through it. I'll see if I can identify it as that may help. I'll report back when I have done some tests. Many thanks for all the help so far.

7th Jan 2008, 9:31 pm	#6
ProDave Retired Dormant Member Join Date: Sep 2007 Location: Inverness Posts: 24	Re: Gould OS4000 Storage oscilloscope All fixed now. Many thanks. Thanks to your help, I removed the two logic boards into their service position. A task that is infinitely easier than it looks at first. But as it turned out, in my case this was unnecessary. I did all the voltage checks you sugested (except the 3KV as I don't have a meter that goes that high) and all were okay. But the fault was soon found. It turned out to be BR55 which provides the +5V and -3V supplies was O/C. Obvious really that a digital 'scope won't peform if it's main logic power supply voltage is missing. This bridge rectifier is mounted directly on the mains transformer (as are all of them) I missed these two voltage tests on my initial blind testing as their test points on the power supply board were not very clearly marked. (by blind testing, I mean my initial probing around to check power supply voltages without the benefit of a circuit diagram or any other service information) So once again many thanks, my trusty old 'scope lives on.

9th Jan 2008, 1:17 pm	#7
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,873	Re: Gould OS4000 Storage oscilloscope Hi! Good Show! Pleased to be of assistance! I'll post more manual when I've got my PC going again - it's m/b has just died! Chris Williams

9th Jan 2008, 1:21 pm	#8
ProDave Retired Dormant Member Join Date: Sep 2007 Location: Inverness Posts: 24	Re: Gould OS4000 Storage oscilloscope Just a quick follow up. I do notice the replacement bridge rectifier (still mounted on the transformer) runs quite hot. I'm sure the replacement is adequately rated, but I don't like semiconductors that run hot. So in the hope of improving reliability, I am going to mount the new BR on the back panel, so it can benefit from the heatsink.

9th Feb 2008, 7:14 pm	#9
jaegerh Retired Dormant Member Join Date: Jan 2008 Location: Linz, Austria Posts: 10	Re: Gould OS4000 Storage oscilloscope Hi Chris and Dave, I also own a Gould OS4000 with some hiccups. Thanks to search engines I found your thread ... very lucky. Since those few scanned pages from the service manual did already help me some way, I am still missing essential information. I wonder if you could help me out? The error on the scope looks as follows: It seems to work fine, but the x-deflection at the 5ms/div to .1ms/div timebase range is totally offset. The trace is shifted about half a screen to the right. I guess it is just one component common to those timebase settings, or a contact in the rotating switch. But before I open the thing up, I would like to have a look at the schematics and service manual, otherwise I don't think I can trace it down. I would also like to check the calibration if the repair is successful. What I really like about this scope is its fanless design, and I hope I can make it fully operational again. I hope you (especially Chris) can help me out with some more scanned pages.. Thanks, Herbert

9th Feb 2008, 11:25 pm	#10
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,873	Re: Gould OS4000 Storage oscilloscope Hi! More manual coming up tomorrow......!!! Chris Williams

15th Feb 2008, 6:56 pm	#13
jaegerh Retired Dormant Member Join Date: Jan 2008 Location: Linz, Austria Posts: 10	Re: Gould OS4000 Storage oscilloscope Chris, thank you very much for spending the time. I will definitely read through the documents asap, hopefully I have the time next weekend to get to the hardware..I will tell you how it went. Thanks again! Herbert

22nd Feb 2008, 1:36 pm	#14
ProDave Retired Dormant Member Join Date: Sep 2007 Location: Inverness Posts: 24	Re: Gould OS4000 Storage oscilloscope Many thanks Chris. All those files stored away for next time the 'scope breaks down.

29th Feb 2008, 2:10 pm	#18
ProDave Retired Dormant Member Join Date: Sep 2007 Location: Inverness Posts: 24	Re: Gould OS4000 Storage oscilloscope Once again, Many thanks Chris for taking the time and trouble to post all that.

25th Mar 2008, 5:37 pm	#19
jaegerh Retired Dormant Member Join Date: Jan 2008 Location: Linz, Austria Posts: 10	Re: Gould OS4000 Storage oscilloscope Great news folks! I had plenty of time over the easter holidays, and with the complete manual at hand (Thanks Chris!) I started to search the fault. And, voila, one of the hold-off capacitors at switch s6dB showed around 500 Ohms instead of 47pF, thus completely upsetting the bias poins in the timebase sweep generator. Now I am really happy to have it fully functional again; I also cleaned the front panel and knobs from previous owners - the scope looks like new now. Calibration is still missing, but I will have to do that at work one evening - that's where the good test equipment lives. By the way, my Gould 4000 has also the OS4001 Output Unit attached to it, which made access to all boards more complicated. The scope does not work with the OS4001 disconnected. Chris, do you have the manual for that as well? I have no clue how to operate it, but I will probably never use it anyway. I have put together the complete circuit diagrams. The scan alignment was good, I didn't even have to rotate them. Please find the files in the attachment - I tried to keep the image quality while meeting the 1.9Mb upload size constraint. You will need an A3 printer for a legible output. Chris, page 75 is titled 'Interconnections (Contd.)' - is there more to it? Also, the component listing is missing for the interconnection diagram. The faulty capacitor was C92 from that schematic, but fortunately the value was printed on it. Could you please scan that if you have the time? Thanks again for all the effort, you really helped me to a nice success experience - Herbert PS - sorry folks, I experience difficulties attaching files even though they are not too big - hopefully I will be successful later.

26th Mar 2008, 1:21 pm	#20
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,873	Re: Gould OS4000 Storage oscilloscope Hi! Yes, I have repair words for the '4001 thingy but my PC's kicked the bucket again - a friend's going to fix it whilst I'm on holliers next week!!! There's not a lot of it, I'll see if I can get it done before I go to my Sister's at the weekend!!! Chris Williams PS!!! I think I've done all I had but I'll double-check the "interconnections" bits list tonight in case I've missed an odd bit out!!!